The present invention relates to the phosphorylation of substrates to enhance the properties of the substrates and to form new compositions of matter. By "phosphorylation" is meant the creation of O-substituted phosphate (R.sup.1 OPO.sub.3) groups on the surface of a solid substrate.
Metaphosphoric acid (HO--PO.sub.2) and metaphosphates (RO--PO.sub.2) are potentially highly useful sources of phosphate groups, since they are extremely reactive, especially to hydroxyl groups. As used herein, "metaphosphate" refers to the monomeric molecule and not to condensed phosphates or polyphosphates, characterized by the presence of --P--O--P--linkages, which are sometimes referred to as metaphosphates. However, that high degree of reactivity also makes the isolation of metaphosphates impossible; the use of metaphosphates as a phosphorylating agent is therefore difficult to carry out. Thus, use of metaphosphate to phosphorylate substrates is difficult and expensive at best, and has not been practiced on a commercial scale.
It has previously been reported that the system 2,3-oxaphosphabicyclo [2.2.2] oct-5-ene-3-oxide undergoes thermal fragmentation in solution to form, for example, ethyl metaphosphate if an ethoxy group is present on the phosphorus (Quin et al., J. Am. Chem. Soc., Vol. 107, pp. 3389-3390 (1985); Quin et al., Tetrahedron Letters, Vol. 31, No. 44, pp. 6281-6282 (1990)). Ethyl metaphosphate formed in this manner has reportedly been used to phosphorylate the surface of silica gel (Quin et al., J. Chem. Soc., Chem. Commun., pp. 555-556 (1988)).
However, adaptation of this procedure to production of meaningful amounts of phosphorylated product on a commercially realistic basis is not practical because of the expense and time required by the complex starting material. It remains desirable to be able to take advantage of the reactivity of metaphosphate. However, a simple, direct method utilizing metaphosphate, in which the starting materials are available, stable, and adaptable to commercially meaningful application, has heretofore not been known.
It has now been determined that the decomposition of the phosphoramidate of formula (1) defined herein and formation of a phosphorylated substrate follows an elimination-addition mechanism, which finding is confirmed by the observation that the reaction follows first-order kinetics. Accordingly, it has now been determined as set forth below that the phosphorylation proceeds via generation of metaphosphate by thermolysis of the phosphoramidate.